millis()

Description

Returns the number of milliseconds passed since the Arduino board began running the current program. This number will overflow (go back to zero), after approximately 50 days.

Syntax

time = millis()

Parameters

None

Returns

Number of milliseconds passed since the program started. Data type:

unsigned long

Example Code

This example code prints on the serial port the number of milliseconds passed since the Arduino board started running the code itself.

1unsigned long myTime;
2
3    void setup() {
4      Serial.begin(9600);
5    }
6    void loop() {
7      Serial.print("Time: ");
8      myTime = millis();
9
10      Serial.println(myTime); // prints time since program started
11      delay(1000);          // wait a second so as not to send massive amounts of data
12    }

Notes and Warnings

• The return value for millis() is of type

  unsigned long

  , logic errors may occur if a programmer tries to do arithmetic with smaller data types such as

  int

  . Even signed

  long

  may encounter errors as its maximum value is half that of its unsigned counterpart.

• millis() is incremented (for 16 MHz AVR chips and some others) every 1.024 milliseconds, then incrementing by 2 (rather than 1) every 41 or 42 ticks, to pull it back into synch; thus some millis() values are skipped. For accurate timing over short intervals, consider using micros().

• millis() will wrap around to 0 after about 49 days (micros in about 71 minutes).

• Reconfiguration of the microcontroller’s timers may result in inaccurate

  millis()

  readings. The "Arduino AVR Boards" and "Arduino megaAVR Boards" cores use Timer0 to generate

  millis()

  . The "Arduino ARM (32-bits) Boards" and "Arduino SAMD (32-bits ARM Cortex-M0+) Boards" cores use the SysTick timer.

See also

• Blink Without Delay